In recent years, miniaturization of a MISFET (Metal Insulator Semiconductor Field Effect Transistor) is proceeding according to the requirements for downsizing electronic devices, and an associated requirement for a thinning of a gate insulating film is remarkable. However, since a problem of depletion of a polycrystalline silicon gate electrode occurs in accordance with the thinning of the gate insulating film, a technique using a metal gate electrode is used in order to avoid this problem.
In a semiconductor device mounting n-type and p-type MISFETs together, it is required that each of them has appropriate threshold voltage. However, when a metal gate electrode is used, unlike the case of using a polycrystalline silicon gate electrode, it is not possible to use a method in which an impurity is introduced into a gate electrode for adjusting a work function thereof.
As a method of adjusting threshold voltage of a MISFET using a metal gate electrode, a technique is known in which an impurity such as La, etc., is implanted into a gate insulating film, however, a problem that carrier mobility is decreased due to impurity implantation is known. The method, for example, is disclosed in a non-patent literary document of P. D. Kirsch et al., IEDM, 2006, p. 629.
On the other hand, a technique is known in which a metal gate electrode is formed so as to include a stress for generating a strain in a channel region of a MISFET, thereby modulating carrier mobility. This technique, for example, is disclosed in a non-patent literary document of F. Andrieu et al., IEDM Tech. Dig., 2006, p. 641.
In addition, a technique is known in which a direction of an included stress is adjusted by changing a film formation method. This technique, for example, is disclosed in a non-patent literary document of Takeo Matsuki et al., Japanese Journal of Applied Physics, Vol. 46, No. 5B, 2007, p. 3181. According to the technique described in this non-patent literary document, plural metal gates having different directions of the stress included therein can be made of one material. In detail, it is possible to include a tensile stress by forming a metal gate electrode using a CVD (Chemical Vapor Deposition) method, and to include a compressive stress by forming a metal gate electrode using a PVD (Physical Vapor Deposition) method.